An I2C (inter-integrated circuit) method and an SPI (serial peripheral interface) method are widely used because (A) communication by use of the I2C and SPI methods, which are synchronous serial transmission, can be carried out at a higher speed than that by use of non-synchronous serial transmission (serial transmission such as RS-232C) and (B) a plurality of slave devices can be connected.
Specifically, the I2C method is a serial transmission interface specification proposed and disclosed by Royal Philips Electronics. An I2C bus includes two signal lines, i.e., a clock signal line SCL and a data signal line SDA (in addition to GND), and can be connected to a plurality of slave devices. A master device selects one slave device from the plurality of slave devices and designates an address which has been given to the one slave device. Then the master device communicates with the slave device thus designated.
FIG. 6 is a block diagram explaining transmission of data with use of an I2C bus.
As shown in FIG. 6, a master device 52 and slave devices 53 and 54 are connected to each other through an SCL 55 and an SDA 56. The SCL 55 is a clock signal line for transmitting a clock signal and the SDA 56 is a data signal line for transmitting data, addresses, and the like. The slave devices 53 and 54 have own addresses, so that the master device 52 selects one slave device, designates an address of the one slave device, and then communicates with the slave device.